Single reel magnetic tape cartridge with pre-defined tape width difference

ABSTRACT

Provided is a magnetic tape cartridge of a single reel type in which a magnetic tape is wound around a reel, in which the magnetic tape includes a non-magnetic support, and a magnetic layer including a ferromagnetic powder and a binding agent on the non-magnetic support, a tape thickness is equal to or smaller than 5.2 μm, a tape width difference (B−A) between a tape width A at a position of 10 m±1 m from a tape outer end and a tape width B at a position of 50 m±1 m from a tape inner end is 2.4 μm to 12.0 μm, and the tape width A and the tape width B are values measured 100 days from the date of magnetic tape cartridge manufacture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/281,169, filed Feb. 21, 2019, which claimspriority under 35 U.S.C 119 to Japanese Patent Applications No.2018-027623 filed on Feb. 20, 2018, No. 2018-075653 filed on Apr. 10,2018, and No. 2019-003415 filed on Jan. 11, 2019. Each of the aboveapplications is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape cartridge.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for datastorage such as data back-up or archives (for example, seeJP2005-346865A).

The recording and reproducing of signals on the magnetic tape arenormally performed by setting a magnetic tape cartridge accommodating amagnetic tape wound around a reel, on a magnetic tape device which iscalled a drive, causing the magnetic tape to run in the magnetic tapedevice, and bringing a surface of a tape (surface of a magnetic layer)and a magnetic head into contact with each other and to slide on eachother.

SUMMARY OF THE INVENTION

The recording of information on a magnetic tape is normally performed byrecording a magnetic signal on a data band of a magnetic tape.Accordingly, a data track is formed on the data band.

Meanwhile, in a case of reproducing the recorded information, themagnetic tape is caused to run in a magnetic tape device to cause amagnetic head to follow the data track of the magnetic tape, and theinformation recorded on the data track is read. Here, in a case whereaccuracy of the magnetic head following the data track is low, areproducing error may occur.

Meanwhile, an increase in recording capacity (high capacity) of themagnetic tape is required in accordance with a great increase ininformation content in recent years. As means for realizing highcapacity, a technology of decreasing a thickness of the magnetic tape(hereinafter, also referred to as “thinning”) and increasing a length ofthe magnetic tape accommodated in 1 reel of the magnetic tape cartridgeis used. However, according to the studies of the inventors, in a casewhere the thickness of the magnetic tape is decreased, a phenomenon thata reproducing error easily occurs is seen.

Therefore, an object of one aspect of the invention is to achieve bothof thinning of the magnetic tape and prevention of reproducing erroroccurrence.

According to one aspect of the invention, there is provided a magnetictape cartridge of a single reel type in which a magnetic tape is woundaround a reel, in which the magnetic tape includes a non-magneticsupport, and a magnetic layer including a ferromagnetic powder and abinding agent on the non-magnetic support, a tape thickness is equal toor smaller than 5.2 μm, a tape width difference (B−A) between a tapewidth A at a position of 10 m±1 m from a tape outer end and a tape widthB at a position of 50 m±1 m from a tape inner end is 2.4 nm to 12.0 nm,and the tape width A and the tape width B are values measured 100 daysfrom the date of magnetic tape cartridge manufacture.

In one aspect, a tape width deformation rate of the magnetic tapemeasured within 20 minutes, after the magnetic tape is stored in a dryenvironment at a temperature of 52° C. for 24 hours in a state where aload of 100 g is applied to a tape in a longitudinal direction and theload is removed, may be equal to or smaller than 400 ppm. The tape widthdeformation rate is a value obtained by starting the storage describedabove 100 days from the date of magnetic tape cartridge manufacture.

In one aspect, the magnetic tape may include a non-magnetic layerincluding a non-magnetic powder and a binding agent, between thenon-magnetic support and the magnetic layer.

In one aspect, the magnetic tape may include a back coating layerincluding a non-magnetic powder and a binding agent on a surface side ofthe non-magnetic support opposite to a surface side provided with themagnetic layer.

In one aspect, the non-magnetic support may be a polyethylenenaphthalate support.

In one aspect, the non-magnetic support may be an aromatic polyamidesupport.

In one aspect, the non-magnetic support may be a polyethyleneterephthalate support.

According to one aspect of the invention, it is possible to provide amagnetic tape cartridge including a magnetic tape having a thinned tapethickness equal to or smaller than 5.2 nm and capable of preventingoccurrence of a reproducing error during the reproduction of informationrecorded on the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an example of an embodiment of amagnetic tape cartridge of the invention. Magnetic tape cartridge 1comprises a single reel 3 around which is wound a magnetic tape 2.

FIG. 2 is a schematic cross-sectional illustration of an embodiment of amagnetic tape suitable for use with the magnetic tape cartridge of theinvention. The depicted embodiment of a magnetic tape includes anon-magnetic support 13; a magnetic layer 11 including a ferromagneticpowder and a binding agent; a non-magnetic layer 12 including anon-magnetic powder and a binding agent, between the non-magneticsupport and the magnetic layer; and a back coating layer 14 including anon-magnetic powder and a binding agent on a surface side of thenon-magnetic support opposite to a surface side provided with themagnetic layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape Cartridge

One aspect of the invention relates to a magnetic tape cartridge of asingle reel type in which a magnetic tape is wound around a reel, inwhich the magnetic tape includes a non-magnetic support, and a magneticlayer including a ferromagnetic powder and a binding agent on thenon-magnetic support, a tape thickness is equal to or smaller than 5.2μm, a tape width difference (B−A) between a tape width A at a positionof 10 m±1 m from a tape outer end and a tape width B at a position of 50m±1 m from a tape inner end is 2.4 μm to 12.0 μm, and the tape width Aand the tape width B are values measured 100 days from the date ofmagnetic tape cartridge manufacture.

One reason of the occurrence of a reproducing error in a case ofreproducing information recorded on the magnetic tape is a temporalchange f a dimension of the magnetic tape in a width direction from therecording to the reproducing of the information on the magnetic tape.Regarding the dimensional change of the magnetic tape in a widthdirection, in JP2005-346865A described above, an increase in dimensionalstability by providing a reinforcing layer has been proposed (forexample, see paragraphs 0014 and 0054 of JP2005-346865A). In otherwords, this proposal also aims to provide a magnetic tape which ishardly deformed.

In regards to this point, the inventors have made intensive studiesabout the dimensional change of the magnetic tape accommodated in themagnetic tape cartridge and obtained the following new findings.

The magnetic tape cartridge is manufactured by wounding a magnetic tape,which is obtained by slitting a long magnetic tape raw material to havea regulated width, around a reel of the magnetic tape cartridge. As theconfiguration of the cartridge, a single reel type including one reeland a twin reel type including two reels are used, and in recent years,a single reel type magnetic tape cartridge is widely used. The inventorshave made intensive studies about the temporal deformation of themagnetic tape in the single reel type magnetic tape cartridge, and it isclear that a phenomenon of the occurrence of deformations differentdepending on positions, in that a portion close to the reel (innerportion) is deformed to have a wider width compared to an initial stagedue to compressive stress in a tape thickness direction and a portionfar from the reel (outer portion) is deformed to have a narrower widthcompared to the initial stage due to tensile stress in a tapelongitudinal direction, significantly occurs in the thinned magnetictape (specifically, the tape thickness is equal to or smaller than 5.2μm). As the reason thereof, the inventors have surmised that, in a casewhere the magnetic tape is thinned, the compressive stress or thetensile stress applied to each position of the magnetic tape furtherincreases, even in a case where the tension applied to the magnetic tapeis same, and as a result, the deformation to have wider or narrowerwidth compared to the initial stage easily occurs. In addition, in acase where the magnetic tape is thinned for realizing high capacity andthe length of the magnetic tape accommodated in one reel of the magnetictape cartridge is increased, the number of magnetic tapes in themagnetic tape cartridge increases. As a result, it is thought that theinner portion (portion close to the reel) of the magnetic tape iscompressed more strongly, and therefore, it is surmised that thephenomenon that the inner portion is deformed to have wider widthcompared to the initial stage more significantly occurs.

From the above findings, the inventors have thought that the temporaldeformation of the magnetic tape from the recording (data trackformation), which is different depending on the positions as describedabove, makes the magnetic head difficult to follow a data track and thisbecomes a reason of the reproducing error.

Therefore, the inventors have thought that, in a case where thedeformation occurring over time in the magnetic tape cartridge from therecording to the reproducing is caused to occur in advance, theoccurrence of the reproducing error caused by the deformation occurringover time from the recording to the reproducing in the thinned magnetictape can be prevented, and further made intensive studies. This was aresearch based on a technical idea which is completely different from atechnical idea of the related art aiming to provide a magnetic tapewhich is hardly deformed. As a result, the inventors have found that theoccurrence of the reproducing error, in a case of reproducinginformation recorded on a magnetic tape thinned to have a tape thicknessequal to or smaller than 5.2 μm, can be prevented by causing thedeformation to occur in advance so that the tape width difference (B−A)becomes 2.4 μm to 12.0 μm 100 days from the date of magnetic tapecartridge manufacture, and one aspect of the invention has beencompleted. The reason for using the 100th day from the date of magnetictape cartridge manufacture as a reference day is because, in themagnetic tape cartridge of the related art, the deformation in which thetape width difference (B−A) becomes equal to or greater than 2.4 μm doesnot occur 100 days from the date of magnetic tape cartridge manufacture.

However, the above description includes the surmise of the inventors.The surmise of the inventors is also included in the followingdescription. The invention is not limited to such surmise.

Hereinafter, the magnetic tape cartridge will be described.

Configuration of Magnetic Tape Cartridge

The magnetic tape cartridge is a single reel type magnetic tapecartridge. In the single reel type magnetic tape cartridge, a magnetictape is wound around a single reel. Regarding the configuration of themagnetic tape cartridge, a well-known technology regarding the singlereel type magnetic tape cartridge can be applied.

Magnetic Tape

Tape Width Difference (B−A)

In the magnetic tape included in the magnetic tape cartridge, the tapewidth difference (B−A) between a tape width A at a position of 10 m±1 mfrom a tape outer end and a tape width B at a position of 50 m±1 m froma tape inner end is 2.4 μm to 12.0 μm. The tape width A and the tapewidth B are values 100 days from the date of magnetic tape cartridgemanufacture.

Identification (ID) information items such as date of manufacture andthe like are recorded on the magnetic tape cartridge, for productmanagement. In the invention and the specification, the “date ofmagnetic tape cartridge manufacture” indicates the date of manufacturewhich is recorded on the magnetic tape cartridge. Such information isnormally recorded on a radio frequency identifier (RFID) tag which is inthe cartridge, and the date of manufacture (normally, date recorded as“Date of Manufacturer”) can be recognized by reading the RFID tag.Regarding the magnetic tape cartridge in which the tape width difference(B−A) 100 days from the date of magnetic tape cartridge manufacture isin the range described above, the recording of information on themagnetic tape accommodated in the magnetic tape cartridge and thereproducing of the recorded information may be performed on any daybefore the 100th day, may be performed 100 days, or may be performed onany day after the 100th day from the date of magnetic tape cartridgemanufacture. The magnetic tape cartridges having the same product lotnumber are normally manufactured by using the same raw material underthe same manufacturing conditions, and thus, the tape width differences(B−A) 100 days from the date of magnetic tape cartridge manufacture canbe assumed to be the same values. The above point is also applied tovarious physical properties which will be described later, in the samemanner.

A portion which is bonded to a region, where the recording and/orreproducing of information is performed, by bonding means using asplicing tape or the like is not considered as a portion of the magnetictape of which various physical properties such as the tape widthdifference (B−A) are to be measured. For example, in order to draw andwind the magnetic tape from the magnetic tape cartridge, a leader tapemay be bonded to a tape outer end of the magnetic tape. In such a case,the leader tape is not considered as a portion of the magnetic tape ofwhich various physical properties such as the tape width difference(B−A) are to be measured. Accordingly, in a case where the leader tapeis bonded, the tape outer end of the magnetic tape is the end of themagnetic tape on a side to which the leader tape is bonded.

The tape outer end is an end portion of the magnetic tape wound around areel and is farthest from the reel, and a tape width A at a position of10 m±1 m from the tape outer end represents a tape width of a portionwhich is deformed to have a narrower width compared to the initial stagedue to a strong tension over time. Meanwhile, the tape inner end is anend portion which is a starting point of the winding around the reel,and the tape width B at a position of 50 m±1 m from the tape inner endrepresents a tape width of a portion which is deformed to have a widerwidth compared to an initial stage due to strong compression over time.

The magnetic tape cartridge is manufactured by winding the magnetic tapeobtained by slitting a long magnetic tape raw material to have aregulated width, around a reel and accommodating the magnetic tape inthe magnetic tape cartridge. The regulated width is generally ½ inches(0.0127 meters) and the widths of the slit magnetic tape are equivalentwidths at each position. Regarding the equivalent width, a manufacturingerror which may normally occur in the slitting step is allowed. Withrespect to this, as described above, it is thought that deformations ofthe magnetic tape different depending on positions occur over time fromthe recording to the reproducing. However, in the magnetic tapecartridge of the related art, the deformation in which the tape widthdifference (B−A) between the tape width A and the tape width B becomesequal to or greater than 2.4 μm does not occur 100 days from the date ofmagnetic tape cartridge manufacture. With respect to this, it is thoughtthat, by causing the deformation in which the tape width difference(B−A) becomes equal to or greater than 2.4 μm 100 days from the date ofmagnetic tape cartridge manufacture to occur in advance, it is possibleto prevent the occurrence of the reproducing error caused by theoccurrence of the deformation of the magnetic tape different dependingon positions over time from the recording to the reproducing asdescribed above. Meanwhile, in a case where a tape width differencebetween the inner portion and the outer portion of the magnetic tapebefore the information is recorded is excessively great, an error easilyoccurs at the time of the recording. With respect to this, in a casewhere the tape width difference (B−A) is equal to or smaller than 12.0μm 100 days from the date of magnetic tape cartridge manufacture, therecording of information can be easily performed over the total lengthof the magnetic tape accommodated in the magnetic tape cartridge. From aviewpoint of further preventing the occurrence of the reproducing error,the tape width difference (B−A) is preferably equal to or greater than3.0 μm and more preferably equal to or greater than 5.0 μm. Meanwhile,from a viewpoint of further preventing the occurrence of error at thetime of the recording, the tape width difference (B−A) is preferablyequal to or smaller than 11.0 μm.

The tape width difference (B−A) is a value obtained by the followingmethod. The following operation and measurement are performed in anenvironment of a temperature of 20° C. to 25° C. and relative humidityof 40% to 60%.

The magnetic tape wound around the reel is extracted from the magnetictape cartridge 100 days from the date of magnetic tape cartridgemanufacture, and a tape sample having a length of 20 cm and includingthe position of 10 m±1 m from the tape outer end, and a tape samplehaving a length of 20 cm and including the position of 50 m±1 m from thetape inner end are cut out. The tape width of each tape sample ismeasured at the center in a longitudinal direction of the tape sample ina state of being sandwiched between plate-shaped members (for example,slide glass), in order to remove the effect of curl. The measurement ofthe tape width can be performed using a well-known measurement devicecapable of performing dimensional measurement with accuracy of 0.1 μmorder. In addition, the measurement is performed within 20 minutes afterthe magnetic tape is extracted from the magnetic tape cartridge. In eachtape sample, the tape width is respectively measured seven times (N=7),and an arithmetical mean of five measured values excluding the maximumvalue and the minimum value from the measured values obtained in theseven times of measurements is obtained. In a case where a total lengthof the magnetic tape accommodated in the magnetic tape cartridge is 950m, the arithmetical mean obtained as described above is set as a tapewidth (tape width A or tape width B) at each position. On the otherhand, in a case where a total length of the magnetic tape accommodatedin the magnetic tape cartridge is a length other than 950 m, a magnetictape total length is set as L1 (unit: m), the arithmetical mean obtainedas described above is set as W1, and W obtained by Equation:W=(950/L1)×W1 is set as a tape width (tape width A or tape width B) ateach position. The tape width difference (B−A) can be controlled byperforming heat treatment. The heat treatment will be described later indetail.

Tape Width Deformation Rate

In the magnetic tape in which the tape width difference (B−A) 100 daysfrom the date of magnetic tape cartridge manufacture is 2.4 μm to 12.0μm as described above, a tape width deformation rate measured by thefollowing method is preferably equal to or smaller than 400 ppm (partsper million), more preferably equal to or smaller than 390 ppm, evenmore preferably equal to or smaller than 380 ppm, still preferably equalto or smaller than 370 ppm, still more preferably equal to or smallerthan 360 ppm, and still even more preferably equal to or smaller than350 ppm. The tape width deformation rate can be, for example, equal toor greater than 10 ppm, and can also be equal to or greater than 100ppm, equal to or greater than 150 ppm, equal to or greater than 200 ppm,or equal to or greater than 250 ppm. It is thought that, as the tapewidth deformation rate is small, a dimensional change of the magnetictape in the width direction from the recording to the reproducing of theinformation on the magnetic tape is small. Therefore, from a viewpointof further preventing the occurrence of the reproducing error caused bya change in the tape width from the recording to the reproducing, themagnetic tape width deformation rate is preferably small and may be 0ppm. The tape width deformation rate can also be controlled by the heattreatment which will be described later in detail.

The tape width deformation rate is a value obtained by the followingmethod. The following operation and measurement are performed in anenvironment of a temperature of 20° C. to 25° C. and relative humidityof 40% to 60%, except the storage described below.

The magnetic tape wound around the reel is extracted from the magnetictape cartridge 100 days from the date of magnetic tape cartridgemanufacture, a tape sample having a length of 20 cm and including theposition of 10 m±1 m from the tape outer end is cut out, and a tapewidth is obtained by the method described above. This tape width is setas a tape width before storage. The tape width before storage is a valueof a tape sample used for obtaining the tape width difference (B−A)(that is, tape width A obtained as described above), or a value obtainedregarding the tape sample cut out to include the position of 10 m±1 mfrom the tape outer end, from the magnetic tape which is the samemagnetic tape of the tape sample used for obtaining the tape widthdifference (B−A).

The tape sample having a length of 20 cm, of which the tape width beforestorage is obtained, is stored in a dry environment at a temperature of52° C. for 24 hours, in a state where a load of 100 g is applied in atape longitudinal direction, by holding one end portion of this tapesample and hanging a weight of 100 g on the other end portion. The dryenvironment is an environment of relative humidity equal to or smallerthan 10%. The storage is started 100 days from the date of magnetic tapecartridge manufacture. After the storage, a tape width (arithmeticalmean of five measured values excluding the maximum value and the minimumvalue from the measured values obtained in the seven times ofmeasurements) is obtained within 20 minutes after removing the load, inthe same manner as in the method described above. This tape width is setas a tape width after storage.

A value obtained by dividing a difference of tape widths before andafter storage (tape width before storage−tape width after storage) bythe tape width before storage×10⁶ (unit: ppm) is set as the tape widthdeformation rate.

Hereinafter, the magnetic tape included in the magnetic tape cartridgewill be described more specifically.

Tape Thickness

A thickness (total thickness) of the magnetic tape is equal to orsmaller than 5.2 μm. The thinning of the magnetic tape is preferablebecause it causes high capacity. However, in the magnetic tape thinnedto have a thickness equal to or smaller than 5.2 μm, deformationsdifferent depending on positions tend to occur in the magnetic tapecartridge over time as described above, in a case where there is nocountermeasure, and the inventors have thought that this causes theoccurrence of the reproducing error. With respect to this, the magnetictape in which the tape width difference (B−A) 100 days from the date ofmagnetic tape cartridge manufacture is 2.4 μm to 12.0 μm, can bereferred to as a magnetic tape in which the deformation occurring overtime in the magnetic tape cartridge from the recording to thereproducing is caused to occur in advance. Accordingly, it is possibleto prevent the occurrence of the reproducing error, in a case ofreproducing information recorded on the magnetic tape thinned to havethe tape thickness equal to or smaller than 5.2 μm. From a viewpoint ofrealizing higher capacity, the thickness of the magnetic tape ispreferably equal to or smaller than 5.0 μm and more preferably equal toor smaller than 4.8 μm. In addition, from a viewpoint of ease ofhandling, the thickness of the magnetic tape is preferably equal to orgreater than 3.0 μm and more preferably equal to or greater than 3.5 μm.

The tape thickness is a value obtained by the following method.

The magnetic tape wound around the reel is extracted from the magnetictape cartridge 100 days from the date of magnetic tape cartridgemanufacture, 10 tape samples (for example, length of 5 to 10 cm) are cutout from a random portion of the magnetic tape, these tape samples areoverlapped, and the thickness is measured. A value which is one tenth ofthe measured thickness (thickness per one tape sample) is set as thetape thickness. The thickness measurement can be performed using awell-known measurement device capable of performing the thicknessmeasurement at 0.1 μm order. This tape thickness may be obtained byusing the magnetic tape used for obtaining the tape width difference(B−A) and/or the tape width deformation rate, and may be obtained byusing a magnetic tape cut out from the magnetic tape cartridge havingthe product lot number same as the magnetic tape cartridge, in which themagnetic tape used for obtaining the tape width difference (B−A) and/orthe tape width deformation rate is accommodated.

In addition, various thicknesses such as the thickness of the magneticlayer can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction isexposed with an ion beam and the observation of the exposed crosssection is performed using a scanning electron microscope. Variousthicknesses can be obtained as the arithmetical mean of the thicknessesobtained at two random portions in the cross section observation.Alternatively, various thicknesses can be obtained as a designedthickness calculated under the manufacturing conditions.

Non-Magnetic Support

The magnetic tape includes at least a non-magnetic support or a magneticlayer. Examples of the non-magnetic support (hereinafter, also simplyreferred to as a “support”) include a polyethylene naphthalate support,a polyamide support, a polyethylene terephthalate support, and apolyamide imide support. These supports can be purchased as acommercially available product or can be manufactured by a well-knownmethod. From hardness, flexibility, and the like, a polyethylenenaphthalate support, a polyamide support, and a polyethyleneterephthalate support are preferable as the support. The polyethylenenaphthalate support means a support including at least a polyethylenenaphthalate layer, and includes a support formed of a single or two ormore layers of polyethylene naphthalate layers, and a support includingone or more other layers in addition to the polyethylene naphthalatelayer. This point is also the same for the other support. In addition,polyamide can have an aromatic skeleton and/or an aliphatic skeleton,and polyamide having an aromatic skeleton (aromatic polyamide) ispreferable, and aramid is more preferable. Corona discharge, plasmatreatment, easy-bonding treatment, or heat treatment may be performedwith respect to these supports in advance.

Magnetic Layer

Ferromagnetic Powder

The magnetic layer includes a ferromagnetic powder and a binding agent.As the ferromagnetic powder included in the magnetic layer,ferromagnetic powder known as ferromagnetic powder used in the magneticlayer of various magnetic recording media can be used. It is preferableto use ferromagnetic powder having a small average particle size, from aviewpoint of improvement of recording density. From this viewpoint, anaverage particle size of the ferromagnetic powder is preferably equal toor smaller than 50 nm, more preferably equal to or smaller than 45 nm,even more preferably equal to or smaller than 40 nm, still preferablyequal to or smaller than 35 nm, still preferably equal to or smallerthan 30 nm, still more preferably equal to or smaller than 25 nm, andstill even more preferably equal to or smaller than 20 nm. Meanwhile,the average particle size of the ferromagnetic powder is preferablyequal to or greater than 5 nm, more preferably equal to or greater than8 nm, even more preferably equal to or greater than 10 nm, stillpreferably equal to or greater than 15 nm, and still more preferablyequal to or greater than 20 nm, from a viewpoint of stability ofmagnetization.

—Hexagonal Ferrite Powder—

As a preferred specific example of the ferromagnetic powder, hexagonalferrite powder can be used. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the invention and the specification, the “hexagonal ferrite powder”is to be understood to mean ferromagnetic powder from which a hexagonalferrite type crystal structure can be detected as a main phase by X-raydiffraction analysis. The main phase is to be understood to mean astructure to which the diffraction peak with the highest intensity in anX-ray diffraction spectrum obtained by X-ray diffraction analysis isassigned. For example, when the diffraction peak with the highestintensity in an X-ray diffraction spectrum obtained by X-ray diffractionanalysis is assigned to the hexagonal ferrite type crystal structure, itshall be determined that the hexagonal ferrite type crystal structure isdetected as a main phase. When a single structure is only detected byX-ray diffraction analysis, this detected structure is determined as amain phase. The hexagonal ferrite type crystal structure at leastcontains, as constitutional atoms, an iron atom, a divalent metal atom,and an oxygen atom. A divalent metal atom is a metal atom which canconvert into a divalent cation as an ion thereof, and examples thereofinclude alkaline earth metal atoms, such as a strontium atom, a bariumatom, and a calcium atom, and a lead atom. In the invention and thespecification, the hexagonal strontium ferrite powder is to beunderstood to mean powder in which a main divalent metal atom containedtherein is a strontium atom, and the hexagonal barium ferrite powder isto be understood to mean powder in which a main divalent metal atomcontained therein is a barium atom. The main divalent metal atom is tobe understood to mean a divalent metal atom having the highest contentin terms of atom % among divalent metal atoms contained in this powder.However, the divalent metal atom does not include rare earth atoms. Inthe invention and the specification, the rare earth atoms are selectedfrom the group consisting of a scandium atom (Sc), an yttrium atom (Y),and a lanthanoid atom. The lanthanoid atom is selected from the groupconsisting of a lanthanum atom (La), a cerium atom (Ce), a praseodymiumatom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samariumatom (Sm), an europium atom (Eu), a gadolinium atom (Gd), a terbium atom(Tb), a dysprosium atom (Dy), a holmium atom (Ho), an erbium atom (Er),a thulium atom (Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is one aspectof the hexagonal ferrite powder will be described in more detail.

The activation volume of the hexagonal strontium ferrite powder ispreferably 800 to 1,500 nm³. The atomized hexagonal strontium ferritepowder showing the activation volume in the range described above issuitable for manufacturing a magnetic tape exhibiting excellentelectromagnetic conversion characteristics. The activation volume of thehexagonal strontium ferrite powder is preferably equal to or greaterthan 800 nm³ and can also be, for example equal to or greater than 850nm³. In addition, from a viewpoint of further improving electromagneticconversion characteristics, the activation volume of the hexagonalstrontium ferrite powder is more preferably equal to or smaller than1,400 nm³, even more preferably equal to or smaller than 1,300 nm³,still preferably equal to or smaller than 1,200 nm³, and still morepreferably equal to or smaller than 1,100 nm³.

The “activation volume” is a unit of magnetization reversal and an indexshowing a magnetic magnitude of the particles. Regarding the activationvolume and an anisotropy constant Ku which will be described laterdisclosed in the invention and the specification, magnetic field sweeprates of a coercivity Hc measurement part at time points of 3 minutesand 30 minutes are measured by using a vibrating sample magnetometer(measurement temperature: 23° C.±1° C.), and the activation volume andthe anisotropy constant Ku are values acquired from the followingrelational expression of Hc and an activation volume V. A unit of theanisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.

Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturationmagnetization (unit: kA/m), k: Boltzmann's constant, T: absolutetemperature (unit: K), V: activation volume (unit: cm³), A: spinprecession frequency (unit: s⁻¹), and t: magnetic field reversal time(unit: s)]

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Thehexagonal strontium ferrite powder can preferably have Ku equal to orgreater than 1.8×10⁵ J/m³, and more preferably have Ku equal to orgreater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontiumferrite powder can be, for example, equal to or smaller than 2.5×10⁵J/m³. However, the high Ku is preferable, because it means high thermalstability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include rare earthatom. In a case where the hexagonal strontium ferrite powder includesrare earth atom, it preferably includes rare earth atom in a content(bulk content) of 0.5 to 5.0 atom %, with respect to 100 atom % of ironatom is 0.5 to 5.0 atom %. In one aspect, the hexagonal strontiumferrite powder which includes rare earth atom can have a rare earth atomsurface portion uneven distribution. The “rare earth atom surfaceportion uneven distribution” of the invention and the specificationmeans that a rare earth atom content with respect to 100 atom % of ironatom in a solution obtained by partially dissolving the hexagonalstrontium ferrite powder with acid (referred to as a “rare earth atomsurface portion content” or simply as a “surface portion content” forrare earth atom) and a rare earth atom content with respect to 100 atom% of iron atom in a solution obtained by totally dissolving thehexagonal strontium ferrite powder with acid (referred to as a “rareearth atom bulk content” or simply as a “bulk content” for rare earthatom) satisfy a ratio of “rare earth atom surface portion content/rareearth atom bulk content>1.0”. The rare earth atom content of thehexagonal strontium ferrite powder is identical to the bulk content.With respect to this, the partial dissolving using acid is to dissolvethe surface portion of particles configuring the hexagonal strontiumferrite powder, and accordingly, the rare earth atom content in thesolution obtained by the partial dissolving is the rare earth atomcontent in the surface portion of the particles configuring thehexagonal strontium ferrite powder. The rare earth atom surface portioncontent satisfying a ratio of “rare earth atom surface portioncontent/rare earth atom bulk content>1.0” means that the rare earthatoms are unevenly distributed in the surface portion (that is, a largeramount of the rare earth atom is present, compared to that inside), inthe particles configuring the hexagonal strontium ferrite powder. Thesurface portion of the specification and the specification means a partof the region of the particles configuring the hexagonal strontiumferrite powder from the inside from the surface.

In a case where the hexagonal strontium ferrite powder includes rareearth atom, the hexagonal strontium ferrite powder preferably includesrare earth atom having a content (bulk content) of 0.5 to 5.0 atom %with respect to 100 atom % of an iron atom. It is surmised that the rareearth atom having the bulk content in the range described above anduneven distribution of the rare earth atom in the surface portion of theparticles configuring the hexagonal strontium ferrite powder contributeto prevention of a decrease in reproducing output during repeatedreproducing. This is surmised that it is because the anisotropy constantKu can be increased due to the rare earth atom having the bulk contentin the range described above included in the hexagonal strontium ferritepowder and the uneven distribution of the rare earth atom in the surfaceportion of the particles configuring the hexagonal strontium ferritepowder. As the value of the anisotropy constant Ku is high, occurrenceof a phenomenon which is so-called thermal fluctuation can be prevented(that is, thermal stability can be improved). By preventing occurrenceof thermal fluctuation, a decrease in reproducing output during repeatedreproducing can be prevented. This is surmised that, the unevendistribution of the rare earth atom in the surface portion of theparticles of the hexagonal strontium ferrite powder may contribute tostabilization of a spin at an iron (Fe) site in a crystal lattice of thesurface portion, thereby increasing the anisotropy constant Ku.

In addition, it is also surmised that, by using the hexagonal strontiumferrite powder having a rare earth atom surface portion unevendistribution as ferromagnetic powder of the magnetic layer, chipping ofthe surface of the magnetic layer due to sliding with a magnetic headcan be prevented. That is, it is surmised that the hexagonal strontiumferrite powder having a rare earth atom surface portion unevendistribution also contributes to improvement of running durability of amagnetic tape. It is surmised that, this is because the unevendistribution of the rare earth atom in the surface of the particlesconfiguring the hexagonal strontium ferrite powder contributes to aninteraction between the surface of the particles and an organicsubstance (for example, binding agent and/or additive) included in themagnetic layer, thereby improving hardness of the magnetic layer.

From a viewpoint of further preventing a decrease in reproducing outputduring repeated running and/or a viewpoint of further improving runningdurability, the rare earth atom content (bulk content) is preferably 0.5to 4.5 atom %, more preferably 1.0 to 4.5 atom %, and even morepreferably 1.5 to 4.5 atom %.

The bulk content is a content obtained by totally dissolving thehexagonal strontium ferrite powder. In the invention and thespecification, the content of the atom is a bulk content obtained bytotally dissolving the hexagonal strontium ferrite powder, unlessotherwise noted. The hexagonal strontium ferrite powder which includesrare earth atom may include only one kind of rare earth atom or mayinclude two or more kinds of rare earth atom, as the rare earth atom. Ina case where two or more kinds of rare earth atom are included, the bulkcontent is obtained from the total of the two or more kinds of rareearth atom. The same also applies to the other components of theinvention and the specification. That is, for a given component, onlyone kind may be used or two or more kinds may be used, unless otherwisenoted. In a case where two or more kinds are used, the content is acontent of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes rareearth atom, the rare earth atom included therein may be any one or morekinds of the rare earth atom. Examples of the rare earth atom preferablefrom a viewpoint of further preventing a decrease in reproducing outputduring repeated reproducing include a neodymium atom, a samarium atom,an yttrium atom, and a dysprosium atom, a neodymium atom, a samariumatom, an yttrium atom are more preferable, and a neodymium atom is evenmore preferable.

In the hexagonal strontium ferrite powder having a rare earth atomsurface portion uneven distribution, a degree of uneven distribution ofthe rare earth atom is not limited, as long as the rare earth atom isunevenly distributed in the surface portion of the particles configuringthe hexagonal strontium ferrite powder. For example, regarding thehexagonal strontium ferrite powder, a ratio of the surface portioncontent of the rare earth atom obtained by partial dissolving performedunder the dissolving conditions exemplified below and the bulk contentof the rare earth atom obtained by total dissolving performed under thedissolving conditions exemplified below, “surface portion content/bulkcontent” is greater than 1.0 and can be equal to or greater than 1.5.The surface portion content satisfying a ratio of “surface portioncontent/bulk content>1.0” means that the rare earth atoms are unevenlydistributed in the surface portion (that is, a larger amount of the rareearth atoms is present, compared to that inside), in the particlesconfiguring the hexagonal strontium ferrite powder. In addition, theratio of the surface portion content of the rare earth atom obtained bypartial dissolving performed under the dissolving conditions exemplifiedbelow and the bulk content of the rare earth atom obtained by totaldissolving performed under the dissolving conditions exemplified below,“surface portion content/bulk content” can be, for example, equal to orsmaller than 10.0, equal to or smaller than 9.0, equal to or smallerthan 8.0, equal to or smaller than 7.0, equal to or smaller than 6.0,equal to or smaller than 5.0, or equal to or smaller than 4.0. However,the “surface portion content/bulk content” is not limited to theexemplified upper limit or the lower limit, as long as the rare earthatom is unevenly distributed in the surface portion of the particlesconfiguring the hexagonal strontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonalstrontium ferrite powder will be described below. Regarding thehexagonal strontium ferrite powder present as the powder, sample powderfor the partial dissolving and the total dissolving are collected frompowder of the same batch. Meanwhile, regarding the hexagonal strontiumferrite powder included in a magnetic layer of a magnetic tape, a partof the hexagonal strontium ferrite powder extracted from the magneticlayer is subjected to the partial dissolving and the other part issubjected to the total dissolving. The extraction of the hexagonalstrontium ferrite powder from the magnetic layer can be performed by amethod disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonalstrontium ferrite powder remaining in the solution can be visuallyconfirmed at the time of the completion of the dissolving. For example,by performing the partial dissolving, a region of the particlesconfiguring the hexagonal strontium ferrite powder which is 10% to 20%by mass with respect to 100% by mass of a total of the particles can bedissolved. On the other hand, the total dissolving means dissolvingperformed until the hexagonal strontium ferrite powder remaining in thesolution is not visually confirmed at the time of the completion of thedissolving.

The partial dissolving and the measurement of the surface portioncontent are, for example, performed by the following method. However,dissolving conditions such as the amount of sample powder and the likedescribed below are merely examples, and dissolving conditions capableof performing the partial dissolving and the total dissolving can berandomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10ml of hydrochloric acid having a concentration of 1 mol/L is held on ahot plate at a set temperature of 70° C. for 1 hour. The obtainedsolution is filtered with a membrane filter having a hole diameter of0.1 μm. The element analysis of the solution obtained as described aboveis performed by an inductively coupled plasma (ICP) analysis device. Bydoing so, the surface portion content of the rare earth atom withrespect to 100 atom % of the iron atom can be obtained. In a case wherea plurality of kinds of rare earth atoms are detected from the elementanalysis, a total content of the entirety of the rare earth atoms is thesurface portion content. The same applies to the measurement of the bulkcontent.

Meanwhile, the total dissolving and the measurement of the bulk contentare, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10ml of hydrochloric acid having a concentration of 4 mol/L is held on ahot plate at a set temperature of 80° C. for 3 hours. After that, theprocess is performed in the same manner as in the partial dissolving andthe measurement of the surface portion content, and the bulk contentwith respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case ofreproducing information recorded on a magnetic tape, it is desirablethat the mass magnetization as of ferromagnetic powder included in themagnetic tape is high. In regards to this point, in hexagonal strontiumferrite powder which includes the rare earth atom but does not have therare earth atom surface portion uneven distribution, as tends tosignificantly decrease, compared to that in hexagonal strontium ferritepowder not including the rare earth atom. With respect to this, it issurmised that, hexagonal strontium ferrite powder having the rare earthatom surface portion uneven distribution is preferable for preventingsuch a significant decrease in as. In one aspect, as of the hexagonalstrontium ferrite powder can be equal to or greater than 45 A·m²/kg andcan also be equal to or greater than 47 A·m²/kg. On the other hand, froma viewpoint of noise reduction, as is preferably equal to or smallerthan 80 A·m²/kg and more preferably equal to or smaller than 60 A·m²/kg.σs can be measured by using a known measurement device capable ofmeasuring magnetic properties such as a vibrating sample magnetometer.Unless stated otherwise, the mass magnetization as is a value measuredat a magnetic field strength of 1,194 kA/m (15 kOe).

With regard to the contents (bulk contents) of the constituting atoms ofthe hexagonal strontium ferrite powder, the content of the strontiumatom in the hexagonal strontium ferrite powder can be, for example, 2.0to 15.0 atom % with respect to 100 atom % of the iron atom. In oneaspect, in the hexagonal strontium ferrite powder, the divalent metalatom included in this powder can be only a strontium atom. In anotheraspect, the hexagonal strontium ferrite powder can also include one ormore kinds of other divalent metal atoms, in addition to the strontiumatom. For example, a barium atom and/or a calcium atom can be included.In a case where the divalent metal atom other than the strontium atom isincluded, a content of a barium atom and a content of a calcium atom inthe hexagonal strontium ferrite powder respectively can be, for example,0.05 to 5.0 atom % with respect to 100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbitetype (also referred to as an “M type”), a W type, a Y type, and a Z typeare known. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be confirmed by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more kinds of crystal structure can be detected bythe X-ray diffraction analysis. For example, in one aspect, in thehexagonal strontium ferrite powder, only the M type crystal structurecan be detected by the X-ray diffraction analysis. For example, the Mtype hexagonal ferrite is represented by a compositional formula ofAFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where thehexagonal strontium ferrite powder has the M type, A is only a strontiumatom (Sr), or in a case where a plurality of divalent metal atoms areincluded as A, the strontium atom (Sr) occupies the hexagonal strontiumferrite powder with the greatest content based on atom % as describedabove. A content of the divalent metal atom in the hexagonal strontiumferrite powder is generally determined according to the type of thecrystal structure of the hexagonal ferrite and is not particularlylimited. The same applies to a content of an iron atom and a content ofan oxygen atom. The hexagonal strontium ferrite powder at least includesan iron atom, a strontium atom, an oxygen atom, may include a rare earthatom, and may or may not include atoms other than these atoms. As anexample, the hexagonal strontium ferrite powder may include an aluminumatom (Al). A content of the aluminum atom can be, for example, 0.5 to10.0 atom % with respect to 100 atom % of the iron atom. From aviewpoint of further preventing a decrease in reproducing output duringrepeated reproducing, the hexagonal strontium ferrite powder includesthe iron atom, the strontium atom, the oxygen atom, and the rare earthatom, and a content of the atoms other than these atoms is preferablyequal to or smaller than 10.0 atom %, more preferably 0 to 5.0 atom %,and may be 0 atom % with respect to 100 atom % of the iron atom. Thatis, in one aspect, the hexagonal strontium ferrite powder may notinclude atoms other than the iron atom, the strontium atom, the oxygenatom, and the rare earth atom. The content shown with atom % describedabove is obtained by converting the content (unit: % by mass) of eachatom obtained by totally dissolving the hexagonal strontium ferritepowder by using the atomic weight. In addition, in the invention and thespecification, a given atom which is “not included” means that thecontent thereof obtained by performing total dissolving and measurementby using an ICP analysis device is 0% by mass. A detection limit of theICP analysis device is generally equal to or smaller than 0.01 ppm(parts per million) based on mass. The expression “not included” is usedas a meaning including that a given atom is included with the amountsmaller than the detection limit of the ICP analysis device. In oneaspect, the hexagonal strontium ferrite powder does not include abismuth atom (Bi).

—Metal Powder—

As a preferred specific example of the ferromagnetic powder,ferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

—ε-Iron Oxide Powder—

As a preferred specific example of the ferromagnetic powder, ε-ironoxide powder can also be used. In the invention and the specification,the “ε-iron oxide powder” is to be understood to mean ferromagneticpowder from which an ε-iron oxide type crystal structure can be detectedas a main phase by X-ray diffraction analysis. For example, when thediffraction peak with the highest intensity in an X-ray diffractionspectrum obtained by X-ray diffraction analysis is assigned to theε-iron oxide type crystal structure, it shall be determined that theε-iron oxide type crystal structure is detected as a main phase. As amethod for producing ε-iron oxide powder, a method for producing ε-ironoxide powder from goethite and a reverse micelle method has been known.Both of the above-described production methods has been publicly known.Moreover, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. 51, pp.S280-S284 and J. Mater. Chem. C, 2013, 1, pp. 5200-5206 can be referredto about a method for producing ε-iron oxide powder where some of Fe aresubstituted with substitutional atoms such as Ga, Co, Ti, Al, and Rh,for example. The method for producing ε-iron oxide powder which can beused as ferromagnetic powder in a magnetic layer of the magnetic tape,however, is not limited to these methods.

The activation volume of the ε-iron oxide powder is preferably 300 to1,500 nm³. The atomized ε-iron oxide powder showing the activationvolume in the range described above is suitable for manufacturing amagnetic tape exhibiting excellent electromagnetic conversioncharacteristics. The activation volume of the ε-iron oxide powder ispreferably equal to or greater than 300 nm³ and can also be, for exampleequal to or greater than 500 nm³. In addition, from a viewpoint offurther improving electromagnetic conversion characteristics, theactivation volume of the ε-iron oxide powder is more preferably equal toor smaller than 1,400 nm³, even more preferably equal to or smaller than1,300 nm³, still preferably equal to or smaller than 1,200 nm³, andstill more preferably equal to or smaller than 1,100 nm³.

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Theε-iron oxide powder can preferably have Ku equal to or greater than3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, forexample, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku ispreferable, because it means high thermal stability, and thus, Ku is notlimited to the exemplified value.

From a viewpoint of increasing reproducing output in a case ofreproducing information recorded on a magnetic tape, it is desirablethat the mass magnetization as of ferromagnetic powder included in themagnetic tape is high. In regards to this point, in one aspect, as ofthe ε-iron oxide powder can be equal to or greater than 8 A·m²/kg andcan also be equal to or greater than 12 A·m²/kg. On the other hand, froma viewpoint of noise reduction, as of the ε-iron oxide powder ispreferably equal to or smaller than 40 A·m²/kg and more preferably equalto or smaller than 35 A·m²/kg.

In the invention and the specification, average particle sizes ofvarious powder such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at a magnification ratio of 100,000 with atransmission electron microscope, the image is printed on photographicprinting paper so that the total magnification of 500,000 to obtain animage of particles configuring the powder. A target particle is selectedfrom the obtained image of particles, an outline of the particle istraced with a digitizer, and a size of the particle (primary particle)is measured. The primary particle is an independent particle which isnot aggregated.

The measurement described above is performed regarding 500 particlesrandomly extracted. An arithmetical mean of the particle size of 500particles obtained as described above is an average particle size of thepowder. As the transmission electron microscope, a transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. can be used, forexample. In addition, the measurement of the particle size can beperformed by well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the invention and thespecification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an aspect in which particles configuring theaggregate are directly in contact with each other, but also includes anaspect in which a binding agent or an additive which will be describedlater is interposed between the particles. A term “particles” is alsoused for describing the powder.

As a method of collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted, (1) in acase where the shape of the particle observed in the particle imagedescribed above is a needle shape, a fusiform shape, or a columnar shape(here, a height is greater than a maximum long diameter of a bottomsurface), the size (particle size) of the particles configuring thepowder is shown as a length of a long axis configuring the particle,that is, a long axis length, (2) in a case where the shape of theparticle is a planar shape or a columnar shape (here, a thickness or aheight is smaller than a maximum long diameter of a plate surface or abottom surface), the particle size is shown as a maximum long diameterof the plate surface or the bottom surface, and (3) in a case where theshape of the particle is a sphere shape, a polyhedron shape, or anunspecified shape, and the long axis configuring the particles cannot bespecified from the shape, the particle size is shown as an equivalentcircle diameter. The equivalent circle diameter is a value obtained by acircle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a short axis, that is, a short axis length of the particles ismeasured in the measurement described above, a value of (long axislength/short axis length) of each particle is obtained, and anarithmetical mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the shortaxis length as the definition of the particle size is a length of ashort axis configuring the particle, in a case of (2), the short axislength is a thickness or a height, and in a case of (3), the long axisand the short axis are not distinguished, thus, the value of (long axislength/short axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average long axislength, and in a case of the definition (2), the average particle sizeis an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50% to 90% by mass and more preferably 60%to 90% by mass. The components other than the ferromagnetic powder ofthe magnetic layer are at least a binding agent and one or more kinds ofadditives may be further randomly included. A high filling percentage ofthe ferromagnetic powder in the magnetic layer is preferable from aviewpoint of improvement of recording density.

Binding Agent and Curing Agent

The magnetic tape is a coating type magnetic tape and includes a bindingagent in the magnetic layer. The binding agent is one or more kinds ofresin. As the binding agent, various resins normally used as a bindingagent of a coating type magnetic recording medium can be used. Forexample, as the binding agent, a resin selected from a polyurethaneresin, a polyester resin, a polyamide resin, a vinyl chloride resin, anacrylic resin obtained by copolymerizing styrene, acrylonitrile, ormethyl methacrylate, a cellulose resin such as nitrocellulose, an epoxyresin, a phenoxy resin, and a polyvinylalkylal resin such as polyvinylacetal or polyvinyl butyral can be used alone or a plurality of resinscan be mixed with each other to be used. Among these, a polyurethaneresin, an acrylic resin, a cellulose resin, and a vinyl chloride resinare preferable. These resins may be homopolymers or copolymers. Theseresins can be used as the binding agent even in the non-magnetic layerand/or a back coating layer which will be described later.

For the binding agent described above, description disclosed inparagraphs 0028 to 0031 of JP2010-024113A can be referred to. An averagemolecular weight of the resin used as the binding agent can be, forexample, 10,000 to 200,000 as a weight-average molecular weight. Theweight-average molecular weight of the invention and the specificationis a value obtained by performing polystyrene conversion of a valuemeasured by gel permeation chromatography (GPC) under the followingmeasurement conditions. The weight-average molecular weight of thebinding agent shown in examples which will be described later is a valueobtained by performing polystyrene conversion of a value measured underthe following measurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

In addition, a curing agent can also be used together with the resinwhich can be used as the binding agent. As the curing agent, in oneaspect, a thermosetting compound which is a compound in which a curingreaction (crosslinking reaction) proceeds due to heating can be used,and in another aspect, a photocurable compound in which a curingreaction (crosslinking reaction) proceeds due to light irradiation canbe used. At least a part of the curing agent is included in the magneticlayer in a state of being reacted (crosslinked) with other componentssuch as the binding agent, by proceeding the curing reaction in themagnetic layer forming step. This point is the same as regarding a layerformed by using a composition, in a case where the composition used forforming the other layer includes the curing agent. The preferred curingagent is a thermosetting compound, polyisocyanate is suitable. Fordetails of the polyisocyanate, descriptions disclosed in paragraphs 0124and 0125 of JP2011-216149A can be referred to, for example. The contentof the curing agent of the magnetic layer forming composition can be,for example, 0 to 80.0 parts by mass with respect to 100.0 parts by massof the binding agent, and can be 50.0 to 80.0 parts by mass, from aviewpoint of improvement of hardness of the magnetic layer.

Additives

The magnetic layer includes ferromagnetic powder and the binding agent,and may include one or more kinds of additives, if necessary. As theadditives, the curing agent described above is used as an example. Inaddition, examples of the additive included in the magnetic layerinclude non-magnetic powder (for example, inorganic powder or carbonblack), a lubricant, a dispersing agent, a dispersing assistant, anantibacterial agent, an antistatic agent, and an antioxidant. Forexample, for the lubricant, descriptions disclosed in paragraphs 0030 to0033, 0035, and 0036 of JP2016-126817A can be referred to. The lubricantmay be included in the non-magnetic layer which will be described later.For the lubricant which may be included in the non-magnetic layer,descriptions disclosed in paragraphs 0030, 0031, 0034, 0035, and 0036 ofJP2016-126817A can be referred to. For the dispersing agent,descriptions disclosed in paragraphs 0061 and 0071 of JP2012-133837A canbe referred to. The dispersing agent may be added to a non-magneticlayer forming composition. For the dispersing agent which may be addedto the non-magnetic layer forming composition, a description disclosedin a paragraph 0061 of JP2012-133837A can be referred to. As thenon-magnetic powder which may be included in the magnetic layer,non-magnetic powder which can function as an abrasive, non-magneticpowder (for example, non-magnetic colloid particles) which can functionas a projection formation agent which forms projections suitablyprotruded from the surface of the magnetic layer, and the like can beused. An average particle size of colloidal silica (silica colloidparticles) shown in the examples which will be described later is avalue obtained by a method disclosed in a measurement method of anaverage particle diameter in a paragraph 0015 of JP2011-048878A. As theadditives, a commercially available product can be suitably selectedaccording to the desired properties or manufactured by a well-knownmethod, and can be used with any amount. As an example of the additivewhich can be used for improving dispersibility of the abrasive in themagnetic layer including the abrasive, a dispersing agent disclosed inparagraphs 0012 to 0022 of JP2013-131285A can be used.

The magnetic layer described above can be provided on the surface of thenon-magnetic support directly or indirectly through the non-magneticlayer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on the surface of the non-magneticsupport or may include a magnetic layer on the surface of thenon-magnetic support directly or indirectly through the non-magneticlayer including the non-magnetic powder and the binding agent. Thenon-magnetic powder used in the non-magnetic layer may be inorganicpowder or organic powder. In addition, carbon black and the like can beused. Examples of the inorganic powder include powder of metal, metaloxide, metal carbonate, metal sulfate, metal nitride, metal carbide, andmetal sulfide. These non-magnetic powder can be purchased as acommercially available product or can be manufactured by a well-knownmethod. For details thereof, descriptions disclosed in paragraphs 0146to 0150 of JP2011-216149A can be referred to. For carbon black which canbe used in the non-magnetic layer, descriptions disclosed in paragraphs0040 and 0041 of JP2010-024113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably 50% to 90% by mass and more preferably 60% to 90% by mass.

In regards to other details of a binding agent or additives of thenon-magnetic layer, the well-known technology regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technology regarding the magneticlayer can be applied.

In the invention and the specification, the non-magnetic layer alsoincludes a substantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Back Coating Layer

The magnetic tape can also include a back coating layer including anon-magnetic powder and a binding agent on a surface side of thenon-magnetic support opposite to the surface side provided with themagnetic layer. The back coating layer preferably includes any one orboth of carbon black and inorganic powder. For the binding agentincluded in the back coating layer and various additives which can berandomly included therein, a well-known technology regarding the backcoating layer can be applied, and a well-known technology regarding theprocess of the magnetic layer and/or the non-magnetic layer can also beapplied. For example, for the back coating layer, descriptions disclosedin paragraphs 0018 to 0020 of JP2006-331625A and page 4, line 65, topage 5, line 38, of U.S. Pat. No. 7,029,774 can be referred to.

Various Thicknesses

The thickness (total thickness) of the magnetic tape is as describedabove.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to asaturation magnetization amount of a magnetic head used, a head gaplength, a recording signal band, and the like, is normally 0.01 μm to0.15 μm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03μm to 0.1 μm, from a viewpoint of realization of high-density recording.The magnetic layer may be at least one layer, or the magnetic layer canbe separated to two or more layers having different magnetic properties,and a configuration regarding a well-known multilayered magnetic layercan be applied. A thickness of the magnetic layer which is separatedinto two or more layers is a total thickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.9 μm and more preferably 0.1 to 0.7 μm.

Manufacturing Step

Preparation of Each Layer Forming Composition

Steps of preparing the composition for forming the magnetic layer, thenon-magnetic layer, or the back coating layer generally include at leasta kneading step, a dispersing step, or a mixing step provided before andafter these steps, if necessary. Each step may be divided into two ormore stages. The components used in the preparation of each layerforming composition may be added at an initial stage or in a middlestage of each step. As the solvent, one kind or two or more kinds ofvarious solvents generally used for manufacturing a coating typemagnetic recording medium can be used. For the solvent, a descriptiondisclosed in a paragraph 0153 of JP2011-216149A can be referred to, forexample. In addition, each component may be separately added in two ormore steps. For example, the binding agent may be separately added inthe kneading step, the dispersing step, and a mixing step for adjustinga viscosity after the dispersion. In order to manufacture the magnetictape, a well-known manufacturing technology can be used in varioussteps. In the kneading step, an open kneader, a continuous kneader, apressure kneader, or a kneader having a strong kneading force such as anextruder is preferably used. For details of the kneading processes,descriptions disclosed in JP1989-106338A (JP-H01-106338A) andJP1989-079274A (JP-H01-079274A) can be referred to. As a disperser, awell-known disperser can be used. The filtering may be performed by awell-known method in any stage for preparing each layer formingcomposition. The filtering can be performed by using a filter, forexample. As the filter used in the filtering, a filter having a holediameter of 0.01 to 3 μm (for example, filter made of glass fiber orfilter made of polypropylene) can be used, for example.

Coating Step

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the surface of the non-magnetic support orperforming multilayer coating with the non-magnetic layer formingcomposition in order or at the same time. The back coating layer can beformed by directly applying the back coating layer forming compositiononto the surface of the non-magnetic support opposite to the surfaceprovided with the non-magnetic layer and/or the magnetic layer (ornon-magnetic layer and/or the magnetic layer is to be provided). For thedetails of the coating for forming each layer, a description disclosedin a paragraph 0066 of JP2010-231843A can be referred to.

Other Steps

For various other steps for manufacturing the magnetic tape, awell-known technology can be applied. For details of the various steps,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to, for example. For example, the coating layer of themagnetic layer forming composition can be subjected to an alignmentprocess, while the coating layer is wet (not dried). For the alignmentprocess, various well-known technologies such as a description disclosedin a paragraph 0067 of JP2010-231843A can be used.

Through various steps, a long magnetic tape raw material can beobtained. The obtained magnetic tape raw material is cut (slit) by awell-known cutter to have a magnetic tape to be wound and mounted on themagnetic tape cartridge. The width is determined according to theregulation and is normally ½ inches (0.0127 meters).

In the magnetic tape obtained by slitting, a servo pattern can also beformed by a well-known method, in order to allow head tracking servo tobe performed in the magnetic tape device (drive). For example, a servopattern can be formed on the magnetic layer which has been subjected todirect current (DC) demagnetization. The direction of thedemagnetization can be a longitudinal direction or a vertical directionof the magnetic tape. Moreover, the direction of magnetization uponforming a servo pattern (i.e., a magnetized region) can be alongitudinal direction or a vertical direction of the magnetic tape.

Heat Treatment

As described above, by causing the deformation which may occur in themagnetic tape cartridge over time from the recording to the reproducing,to occur in advance, it is possible to control the tape widthdifferences (B−A) in the range described above. For this, the magnetictape cut to have the width described above is preferably wound around acore member and is subjected to the heat treatment in the wound state.By this heat treatment, it is possible to cause the deformation whichmay occur in the magnetic tape wound around the reel in the magnetictape cartridge over time from the recording to the reproducing, to occurin advance.

In one aspect, the heat treatment is performed in a state where themagnetic tape is wound around the core member for heat treatment(hereinafter, referred to as a “core for heat treatment”), the magnetictape after the heat treatment is wound around a reel of the magnetictape cartridge, and a magnetic tape cartridge in which the magnetic tapeis wound around the reel can be manufactured.

The core for heat treatment can be formed of metal, a resin, or paper.The material of the core for heat treatment is preferably a materialhaving high rigidity, from a viewpoint of preventing the occurrence of awinding defect such as spoking or the like. From this viewpoint, thecore for heat treatment is preferably formed of metal or a resin. Inaddition, as an index for rigidity, a modulus of bending elasticity ofthe material for the core for heat treatment is preferably equal to orgreater than 0.2 GPa and more preferably equal to or greater than 0.3GPa. Meanwhile, since the material having high rigidity is normallyexpensive, the use of the core for heat treatment of the material havingrigidity exceeding the rigidity capable of preventing the occurrence ofthe winding defect causes the cost increase. By considering theviewpoint described above, the modulus of bending elasticity of thematerial for the core for heat treatment is preferably equal to orsmaller than 250 GPa. The modulus of bending elasticity is a valuemeasured based on international organization for standardization (ISO)178 and the modulus of bending elasticity of various materials is wellknown. In addition, the core for heat treatment can be a solid or hollowcore member. In a case of a hollow state, a wall thickness is preferablyequal to or greater than 2 mm, from a viewpoint of maintaining therigidity. In addition, the core for heat treatment may include or maynot include a flange.

The magnetic tape having a length equal to or greater than a length tobe finally accommodated in the magnetic tape cartridge (hereinafter,referred to as a “final product length” is prepared as the magnetic tapewound around the core for heat treatment, and it is preferable toperform the heat treatment by placing the magnetic tape in the heattreatment environment, in a state where the magnetic tape is woundaround the core for heat treatment. The magnetic tape length woundaround the core for heat treatment is equal to or greater than the finalproduct length, and is preferably the “final product length+α”, from aviewpoint of ease of winding around the core for heat treatment. α ispreferably equal to or greater than 5 m, from a viewpoint of ease of thewinding. The tension in a case of winding around the core for heattreatment is preferably equal to or greater than 0.1 N (newton), fromviewpoints of ease of the winding, ease of adjusting the tape widthdifference (B−A) by heat treatment, and manufacturing suitability. Inaddition, from a viewpoint of preventing the occurrence of excessivedeformation, the tension in a case of winding around the core for heattreatment is preferably equal to or smaller than 1.5 N and morepreferably equal to or smaller than 1.0 N. An outer diameter of the corefor heat treatment is preferably equal to or greater than 20 mm and morepreferably equal to or greater than 40 mm, from viewpoints of ease ofthe winding and preventing coiling (curl in longitudinal direction).Meanwhile, from a viewpoint of ease of adjusting the tape widthdifference (B−A) to be in the range described above, the outer diameterof the core for heat treatment is preferably equal to or smaller than100 mm and more preferably equal to or smaller than 90 mm. A width ofthe core for heat treatment may be equal to or greater than the width ofthe magnetic tape wound around this core. In addition, after the heattreatment, in a case of detaching the magnetic tape from the core forheat treatment, it is preferable that the magnetic tape and the core forheat treatment are sufficiently cooled and magnetic tape is detachedfrom the core for heat treatment, in order to prevent the occurrence ofthe tape deformation which is not intended during the detachingoperation. It is preferable the detached magnetic tape is wound aroundanother core temporarily (referred to as a “core for temporarywinding”), and the magnetic tape is wound around a reel (generally,outer diameter is appropriately 40 to 50 mm) of the magnetic tapecartridge from the core for temporary winding. Accordingly, arelationship between the inside and the outside with respect to the corefor heat treatment of the magnetic tape in a case of the heat treatmentcan be maintained and the magnetic tape can be wound around the reel ofthe magnetic tape cartridge. Regarding the details of the core fortemporary winding and the tension in a case of winding the magnetic tapearound the core, the description described above regarding the core forheat treatment can be referred to. In an aspect in which the heattreatment is subjected to the magnetic tape having a length of the“final product length+α”, the length corresponding to “+α” may beextracted in any stage. For example, in one aspect, the magnetic tapehaving the final product length may be wound around the reel of themagnetic tape cartridge from the core for temporary winding and theremaining length corresponding the “+α” may be extracted. From aviewpoint of decreasing the amount of the portion to be cut out andremoved, the a is preferably equal to or smaller than 20 m.

The specific aspect of the heat treatment performed in a state of beingwound around the core member as described above is described below.

An atmosphere temperature for performing the heat treatment(hereinafter, referred to as “heat treatment temperature”) is preferablyequal to or higher than 40° C. and more preferably equal to or higherthan 50° C. On the other hand, from a viewpoint of preventing theexcessive deformation, the heat treatment temperature is preferablyequal to or lower than 75° C., more preferably equal to or lower than70° C., and even more preferably equal to or lower than 65° C.

A weight absolute humidity of the atmosphere for performing the heattreatment is preferably equal to or greater than 0.1 g/kg Dry air andmore preferably equal to or greater than 1 g/kg Dry air. The atmospherein which the weight absolute humidity is in the range described above ispreferable, because it can be prepared without using a special devicefor decreasing moisture. On the other hand, the weight absolute humidityis preferably equal to or smaller than 70 g/kg Dry air and morepreferably equal to or smaller than 66 g/kg Dry air, from a viewpoint ofpreventing a deterioration in workability. The heat treatment time ispreferably equal to or longer than 0.3 hours and more preferably equalto or longer than 0.5 hours. In addition, the heat treatment time spreferably equal to or shorter than 48 hours, from a viewpoint ofproduction efficiency.

By performing the heat treatment as described above, it is possible tomanufacture the magnetic tape cartridge including the magnetic tapehaving the tape width difference (B−A) of 2.4 μm to 12.0 μm, as a value100 days from the date of magnetic tape cartridge manufacture. The tapewidth of the magnetic tape subjected to the heat treatment generallybecomes wider from the tape outer end towards the inner end.Accordingly, in a case of measuring the tape width of the tape samplecollected from a random position between the measurement position of thetape width A and the measurement position of the tape width B, the valueis normally a value greater than the tape width A and smaller than thetape width B, as the value 100 days from the date of magnetic tapecartridge manufacture.

That is, according to one aspect, it is possible to provide amanufacturing method of the magnetic tape cartridge according to oneaspect of the invention. In such a manufacturing method, by cutting outthe magnetic tape having an equivalent width from the magnetic tape rawmaterial and performing the heat treatment of the cut-out magnetic tapein a state of being wound around the core member, it is possible tocause the magnetic tape to be deformed so that the tape width difference(B−A) is 2.4 μm to 12.0 μm as a value 100 days from the date of magnetictape cartridge manufacture. The details of the manufacturing method areas described above.

In one aspect, the shipping date of the magnetic tape cartridge (datewhen the magnetic tape cartridge is shipped as a product from thefactory) can be any day in the period from the date of magnetic tapecartridge manufacture to the 100th day. Even in a case where themagnetic tape cartridge shipped in the period described above is used inan initial stage after the shipping, it is possible to prevent theoccurrence of the reproducing error. It is preferable to ship themagnetic tape cartridge in the period from the date of magnetic tapecartridge manufacture to the 100th day, from a viewpoint that theinventory storage for a long period of time is not necessary.

The magnetic tape cartridge can be mounted on the magnetic tape deviceincluding a magnetic head and can be used for performing the recordingand/or reproducing of the information. In the invention and thespecification, the “magnetic tape device” means a device capable ofperforming at least one of the recording of information on the magnetictape or the reproducing of information recorded on the magnetic tape.Such a device is generally called a drive. The magnetic head included inthe magnetic tape device can be a recording head capable of performingthe recording of information on the magnetic tape, and can also be areproducing head capable of performing the reproducing of informationrecorded on the magnetic tape. In addition, in one aspect, the magnetictape device can include both of a recording head and a reproducing headas separate magnetic heads. In another aspect, the magnetic headincluded in the magnetic tape device can also have a configuration ofincluding both of a recording element and a reproducing element in onemagnetic head. As the reproducing head, a magnetic head (MR head)including a magnetoresistive (MR) element capable of reading informationrecorded on the magnetic tape with excellent sensitivity as thereproducing element is preferable. As the MR head, various well-known MRheads (for example, a giant magnetoresistive (GMR) head or a tunnelmagnetoresistive (TMR) head) can be used. In addition, the magnetic headwhich performs the recording of information and/or the reproducing ofinformation may include a servo pattern reading element. Alternatively,as a head other than the magnetic head which performs the recording ofinformation and/or the reproducing of information, a magnetic head(servo head) including a servo pattern reading element may be includedin the magnetic tape device.

In the magnetic tape device, the recording of information on themagnetic tape and/or the reproducing of information recorded on themagnetic tape can be performed by bringing the surface of the magneticlayer of the magnetic tape into contact with the magnetic head andsliding. The magnetic tape device can include the magnetic tapecartridge according to one aspect of the invention to be attachable anddetachable, and well-known technologies can be applied for the otherconfigurations.

The magnetic tape device includes the magnetic tape cartridge accordingto one aspect of the invention. Therefore, it is possible to prevent theoccurrence of the reproducing error in a case of reproducing theinformation recorded on the magnetic tape.

EXAMPLES

Hereinafter, one aspect of the invention will be described withreference to examples. However, the invention is not limited to aspectsshown in the examples. “Parts” and “%” in the following description mean“parts by mass” and “% by mass”, unless otherwise noted. “eq” is anequivalent which is a unit which cannot be converted into the SI unit.

In addition, the various steps and operations described below wereperformed in an environment of a temperature of 20° C. to 25° C. andrelative humidity of 40% to 60%, unless otherwise noted.

In Table 1, BaFe indicates hexagonal ferrite barium powder, SrFeindicates hexagonal ferrite strontium powder, ε-iron oxide indicatesε-iron oxide powder, PEN indicates a polyethylene naphthalate support,PA indicates an aromatic polyamide support, and PET indicates apolyethylene terephthalate support.

Example 1

(1) Preparation of Alumina Dispersion

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a polyester polyurethaneresin including a SO₃Na group as a polar group (UR-4800 manufactured byToyobo Co., Ltd. (polar group amount: 80 meq/kg)), and 570.0 parts of amixed solution of methyl ethyl ketone and cyclohexanone (mass ratio of1:1) as a solvent were mixed with 100.0 parts of alumina powder (HIT-80manufactured by Sumitomo Chemical Co., Ltd.) having a gelatinizationratio of 65% and a Brunauer-Emmett-Teller (BET) specific surface area of20 m²/g, and dispersed in the presence of zirconia beads by a paintshaker for 5 hours. After the dispersion, the dispersion liquid and thebeads were separated by a mesh and an alumina dispersion was obtained.

(2) Magnetic Layer Forming Composition List

Magnetic Liquid

-   -   Ferromagnetic powder: 100.0 parts

Ferromagnetic hexagonal barium ferrite powder having average particlesize (average plate diameter) of 21 nm

-   -   SO3Na group-containing polyurethane resin: 14.0 parts    -   Weight-average molecular weight: 70,000, SO3Na group: 0.2 meq/g    -   Cyclohexanone: 150.0 parts    -   Methyl ethyl ketone: 150.0 parts    -   Abrasive Solution    -   Alumina dispersion prepared in the section (1): 6.0 parts    -   Silica Sol (projection forming agent liquid)    -   Colloidal silica (Average particle size: 120 nm) 2.0 parts    -   Methyl ethyl ketone: 1.4 parts    -   Other Components    -   Stearic acid: 2.0 parts    -   Stearic acid amide: 0.2 parts    -   Butyl stearate: 2.0 parts

Polyisocyanate (CORONATE (registered trademark) L manufactured by TosohCorporation): 2.5 parts

-   -   Finishing Additive Solvent    -   Cyclohexanone: 200.0 parts    -   Methyl ethyl ketone: 200.0 parts

(3) Non-Magnetic Layer Forming Composition List

-   -   Non-magnetic inorganic powder: α-iron oxide: 100.0 parts    -   Average particle size (average long axis length): 0.15 μm    -   Average acicular ratio: 7    -   BET specific surface area: 52 m²/g    -   Carbon black: 20.0 parts    -   Average particle size: 20 nm    -   SO3Na group-containing polyurethane resin: 18.0 parts    -   Weight-average molecular weight: 70,000, SO3Na group: 0.2 meq/g    -   Stearic acid: 2.0 parts    -   Stearic acid amide: 0.2 parts    -   Butyl stearate: 2.0 parts    -   Cyclohexanone: 300.0 parts    -   Methyl ethyl ketone: 300.0 parts

(4) Back Coating Layer Forming Composition List

-   -   Carbon black: 100.0 parts    -   Dibutyl phthalate (DBP) oil absorption: 74 cm³/100 g    -   Nitrocellulose: 27.0 parts    -   Polyester polyurethane resin including sulfonic acid group        and/or salt thereof: 62.0 parts    -   Polyester resin: 4.0 parts    -   Alumina powder (BET specific surface area: 17 m²/g): 0.6 parts    -   Methyl ethyl ketone: 600.0 parts    -   Toluene: 600.0 parts    -   Polyisocyanate (CORONATE L manufactured by Tosoh Corporation):        15.0 parts

(5) Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod. The magnetic liquid was prepared by dispersing(beads-dispersing) each component by using a batch type vertical sandmill for 24 hours. Zirconia beads having a bead diameter of 0.5 mm wereused as the dispersion beads. The prepared magnetic liquid, the abrasivesolution, and other components (silica sol, other components, andfinishing additive solvent) were mixed with each other andbeads-dispersed for 5 minutes by using the sand mill, and the treatment(ultrasonic dispersion) was performed with a batch type ultrasonicdevice (20 kHz, 300 W) for 0.5 minutes. After that, the obtained mixedsolution was filtered by using a filter having a hole diameter of 0.5μm, and the magnetic layer forming composition was prepared.

The non-magnetic layer forming composition was prepared by the followingmethod. The components described above excluding the lubricant (stearicacid, stearic acid amide, and butyl stearate) were kneaded and dilutedby an open kneader, and subjected to a dispersion process with atransverse beads mill disperser. After that, the lubricant (stearicacid, stearic acid amide, and butyl stearate) was added, and stirred andmixed with a dissolver stirrer, and a non-magnetic layer formingcomposition was prepared.

The back coating layer forming composition was prepared by the followingmethod. The components excluding polyisocyanate were introduced in adissolver stirrer and stirred at a circumferential speed of 10 msec for30 minutes, and the dispersion process was performed with a transversebeads mill disperser. After that, polyisocyanate was added, and stirredand mixed with a dissolver stirrer, and a back coating layer formingcomposition was prepared.

(6) Manufacturing Method of Magnetic Tape and Magnetic Tape Cartridge

The non-magnetic layer forming composition prepared in the section (5)was applied to a surface of a support having the kind and thicknessshown in Table 1 so that the thickness after the drying becomes athickness shown in Table 1 and was dried to form a non-magnetic layer.Then, the magnetic layer forming composition prepared in the section (5)was applied onto the non-magnetic layer so that the thickness after thedrying becomes a thickness shown in Table 1, and a coating layer wasformed. After that, a homeotropic alignment process was performed byapplying a magnetic field having a magnetic field strength of 0.3 T in avertical direction with respect to a surface of a coating layer, whilethe coating layer of the magnetic layer forming composition is wet (notdried), and was dried to form a magnetic layer. After that, the backcoating layer forming composition prepared in the section (5) wasapplied to the surface of the support shown in Table 1 on a sideopposite to the surface where the non-magnetic layer and the magneticlayer were formed, so that the thickness after the drying becomes athickness shown in Table 1, and was dried to form a back coating layer.

After that, a surface smoothing treatment (calender process) wasperformed by using a calender roll configured of only a metal roll, at aspeed of 100 m/min, linear pressure of 294 kN/m (300 kg/cm), and acalender temperature (surface temperature of a calender roll) of 90° C.

Then, the heat treatment was performed by storing the long magnetic taperaw material in a heat treatment furnace at the atmosphere temperatureof 70° C. (heat treatment time: 36 hours). After the heat treatment, themagnetic tape was obtained by slitting the long magnetic tape rawmaterial to have a width of ½ inches (0.0127 meters). By recording aservo signal on a magnetic layer of the obtained magnetic tape with acommercially available servo writer, the magnetic tape including a databand, a servo band, and a guide band in the disposition according to alinear-tape-open (LTO) Ultrium format, and including a servo pattern(timing-based servo pattern) having the disposition and shape accordingto the LTO Ultrium format on the servo band was obtained.

The magnetic tape (length of 960 m) after recording the servo signal waswound around the core for heat treatment, and the heat treatment wasperformed in a state of being wound around this core. As the core forheat treatment, a solid core member (outer diameter: 50 mm) formed of aresin and having 0.8 GPa of a modulus of bending elasticity was used,and the tension at the time of the winding was set as 0.6 N. The heattreatment was performed at the heat treatment temperature shown in Table1 for 5 hours. The weight absolute humidity in the atmosphere in whichthe heat treatment was performed was 10 g/kg Dry air.

After the heat treatment, the magnetic tape and the core for heattreatment were sufficiently cooled, the magnetic tape was extracted fromthe core for heat treatment and wound around the core for temporarywinding, and then, the magnetic tape having the final product length(950 m) was wound around a reel (reel outer diameter: 44 mm) of themagnetic tape cartridge (LTO Ultrium 7 data cartridge) from the core fortemporary winding. The remaining length of 10 m was cut out and theleader tape based on section 9 of Standard ECMA (European ComputerManufacturers Association)-319 (June 2001) Section 3 was bonded to theend of the cut-out side by using a commercially available splicing tape.As the core for temporary winding, a solid core member having the sameouter diameter and formed of the same material as the core for heattreatment was used, and the tension at the time of winding was set as0.6 N.

As described above, a single reel type magnetic tape cartridge ofExample 1 in which the magnetic tape having a length of 950 m was woundaround a reel was manufactured.

In the examples, the comparative examples, and reference examples, twomagnetic tape cartridges were manufactured, one of them was used in theevaluation which will be described later, and the other one was used ina recording and reproducing test which will be described later. The datewhen the magnetic tape was accommodated in the magnetic tape cartridgewas recorded on a RFID tag in each magnetic tape cartridge as the dateof magnetic tape cartridge manufacture (date of manufacturer).

Examples 2 to 6

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that the heat treatment performed in a state where themagnetic tape was wound around the core for heat treatment, wasperformed at a heat treatment temperature shown in Table 1.

Example 7

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that a support shown in Table 1 was used as thesupport, and the heat treatment performed in a state where the magnetictape was wound around the core for heat treatment, was performed at aheat treatment temperature shown in Table 1.

Example 8

A magnetic tape cartridge was manufactured in the same manner as inExample 7, except that heat treatment performed in a state where themagnetic tape was wound around the core for heat treatment, wasperformed at a heat treatment temperature shown in Table 1.

Example 9

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that a support shown in Table 1 was used as thesupport, and the heat treatment performed in a state where the magnetictape was wound around the core for heat treatment, was performed at aheat treatment temperature shown in Table 1.

Example 10

A magnetic tape cartridge was manufactured in the same manner as inExample 9, except that heat treatment performed in a state where themagnetic tape was wound around the core for heat treatment, wasperformed at a heat treatment temperature shown in Table 1.

Example 11

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that the ferromagnetic powder was changed to thehexagonal strontium ferrite powder prepared by the following method.

(Preparation Method of Hexagonal Strontium Ferrite Powder)

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixedwith a mixer to obtain a raw material mixture.

The obtained raw material mixture was melted in a platinum crucible at amelting temperature of 1,390° C., a tap hole provided on the bottom ofthe platinum crucible was heated while stirring the melted liquid, andthe melted liquid was extracted in a rod shape at approximately 6 g/sec.The extracted liquid was rolled and rapidly cooled with a water-cooledtwin roller to manufacture an amorphous material.

280 g of the manufactured amorphous material was put into an electricfurnace and heated to 635° C. (crystallization temperature) at a rate oftemperature increase of 3.5° C./min, and held at the same temperaturefor 5 hours, to precipitate (crystallize) hexagonal strontium ferriteparticles.

Then, a crystalline material obtained above including the hexagonalstrontium ferrite particles was coarsely crushed with a mortar andsubjected to a dispersion process with a paint shaker for 3 hours, byadding 1,000 g of zirconia beads having a particle diameter of 1 mm and800 ml of acetic acid having a concentration of 1% in a glass bottle.After that, the obtained dispersion liquid was separated from the beadsand put into a stainless steel beaker. A dissolving process of the glasscomponent was performed by leaving the dispersion liquid at a liquidtemperature of 100° C. for 3 hours, the precipitation was performed witha centrifugal separator, decantation was repeated for washing, and theresultant material was dried in a heating furnace at a temperature inthe furnace of 110° C. for 6 hours, thereby obtaining hexagonalstrontium ferrite powder.

The hexagonal strontium ferrite powder obtained above had an averageparticle size of 18 nm, an activation volume of 902 nm³, an anisotropyconstant of 2.2×10⁵ J/m³, and a mass magnetization as of 49 A·m²/kg.

12 mg of sample powder was collected from the hexagonal strontiumferrite powder obtained above, element analysis of filtrate obtained bypartially dissolving the sample powder under the dissolving conditionsexemplified above was performed by the ICP analysis device, and thesurface portion content of neodymium atom was obtained.

Separately, 12 mg of sample powder was collected from the hexagonalstrontium ferrite powder obtained above, element analysis of filtrateobtained by totally dissolving the sample powder under the dissolvingconditions exemplified above was performed by the ICP analysis device,and the surface portion content of neodymium atom was obtained.

In the hexagonal strontium ferrite powder, the content (bulk content) ofneodymium atom with respect to 100 atom % of iron atom was 2.9 atom %,and the surface portion content of neodymium atom was 8.0 atom %. The“surface portion content/bulk content”, that is a ratio of the surfaceportion content to the bulk content, was 2.8. It was confirmed that theneodymium atom was unevenly distributed in the surface portion of theparticles.

The X-ray diffraction analysis of the powder obtained above wasperformed by scanning with a CuKα ray at a voltage of 45 kV andintensity of 40 mA and by measuring X-ray diffraction pattern under theconditions. By the X-ray diffraction analysis it was confirmed that thepowder obtained above showed the crystal structure of hexagonal ferrite.The powder obtained above showed a crystal structure of magnetoplumbitetype (M type) hexagonal ferrite. In addition, a crystal phase detectedby the X-ray diffraction analysis was a magnetoplumbite type singlephase.

-   -   PANalytical X'Pert Pro diffractometer, PIXcel detector    -   Soller slit of incident beam and diffraction beam: 0.017 radians    -   Fixed angle of dispersion slit: ¼ degrees    -   Mask: 10 mm    -   Scattering prevention slit: ¼ degrees    -   Measurement mode: continuous    -   Measurement time per 1 stage: 3 seconds    -   Measurement speed: 0.017 degrees per second    -   Measurement step: 0.05 degrees

Example 12

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that the ferromagnetic powder was changed to thehexagonal strontium ferrite powder prepared by the following method.

(Preparation Method of Hexagonal Strontium Ferrite Powder)

At first, 1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g ofAl(OH)₃, 34 g of CaCO₃, and 141 g of BaCO₃ were weighed, and were thenmixed with a mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1380° C., a tap hole provided on the bottomof the platinum crucible was heated while stirring the melted liquid,and the melted liquid was extracted in a rod shape at approximately 6g/sec. The extracted liquid was rolled and rapidly cooled with awater-cooled twin roller to manufacture an amorphous material.

Then, 280 g of the obtained amorphous material was placed in an electricfurnace, the temperature in the electric furnace was raised to 645° C.(crystallization temperature), and the amorphous material was stillstood in the electric furnace for 5 hours at the same temperature, toprecipitate (crystalize) hexagonal strontium ferrite particles.

Subsequently, the above-obtained crystal containing hexagonal strontiumferrite particles was roughly ground in a mortar, and the groundcrystals was put in a glass bottle, together with 1000 g of zirconiabeads having a particle diameter of 1 mm and 800 ml of acetic acidhaving a concentration of 1% and were subjected to a dispersiontreatment for 3 hours with a paint shaker. Thereafter, the obtaineddispersion was separated from the beads and put in a stainless beaker.The dispersion was stood still at a liquid temperature of 100° C. for 3hours to dissolve a glass component, and thereafter centrifuged in acentrifugal separator to precipitation and were repeatedly decanted towash the precipitated matter and the precipitated matter is dried in afurnace at an in-furnace temperature of 110° C. for 6 hours, to obtainhexagonal strontium ferrite powder.

The obtained hexagonal strontium ferrite powder had an average particlesize of 19 nm, an activation volume of 1102 nm³, an anisotropy constantKu of 2.0×10⁵ J/m³, and a mass magnetization as of 50 A·m²/kg.

Example 13

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that the ferromagnetic powder was changed to theε-iron oxide powder prepared by the following method.

(Preparation Method of ε-Iron Oxide Powder)

A solution was prepared by dissolving 8.3 g of iron(III) nitratenonahydrate, 1.3 g of gallium(III) nitrate octahydrate, 190 mg ofcobalt(II) nitrate hexahydrate, 150 mg of titanium(IV) sulfate, and 1.5g of polyvinylpyrrolidone (PVP) in 90 g of pure water. While stirringthe solution using a magnetic stirrer, 4.0 g of aqueous ammonia solutionhaving a concentration of 25% was then added to the solution in theatmosphere under a condition of an ambient temperature of 25° C. andstirred for subsequent 2 hours under the same ambient temperature of 25°C. A citric acid solution, which was obtained by dissolving 1 g ofcitric acid in 9 g of pure water, was added to the obtained solution,and the obtained mixture was then stirred for 1 hour. Powderprecipitated after the stirring was collected by centrifugal separation,washed with pure water, and dried in a furnace at an in-furnacetemperature of 80° C.

To the dried powder, 800 g of pure water was added to disperse thepowder in water again for preparing a dispersion. The obtaineddispersion was heated at a liquid temperature of 50° C., and 40 g ofaqueous ammonia solution having a concentration of 25% was addeddropwise thereto while stirring the dispersion. The dispersion wasstirred for 1 hour while maintaining the liquid temperature at 50° C.,and 14 mL of tetraethoxysilane (TEOS) was then added dropwise to thedispersion, and the obtained mixture was then stirred for 24 hours. Tothe obtained reaction solution, 50 g of ammonium sulfate was added, andprecipitated powder was then collected by centrifugal separation, washedwith pure water, and dried in a furnace at an in-furnace temperature of80° C., to obtain a ferromagnetic powder precursor.

The obtained ferromagnetic powder precursor was put in a furnace at anin-furnace temperature of 1000° C. in the atmosphere and heat-treatedfor 4 hours.

The heat-treated ferromagnetic powder precursor was introduced into a 4mol/L aqueous sodium hydroxide (NaOH) solution, and then stirred for 24hours while maintaining a liquid temperature at 70° C. to removeimpurity silicate compound from the ferromagnetic powder precursorsubjected to the heat treatment.

Thereafter, the ferromagnetic powder from which a silicate compound hasbeen removed was collected by a centrifugal separation and washed withpure water, to obtain ferromagnetic powder.

The composition of the obtained ferromagnetic powder was analyzed byinductively coupled plasma-optical emission spectrometry (ICP-OES) andwas found to be Ga, Co, and Ti substitution-type ε-iron oxide(ε-Ga_(0.58)Fe_(1.42)O₃). Moreover, the obtained ferromagnetic powderwas analyzed by X-ray diffraction analysis under the same conditions asdescribed in Example 11 described above, and it was confirmed from peaksin the X-ray diffraction pattern that the obtained ferromagnetic powderdid not have crystal structures of α phase and γ phase and had a singlecrystal structure of ε phase (ε-iron oxide type crystal structure).

The obtained ε-iron oxide powder had an average particle size of 12 nm,an activation volume of 746 nm³, an anisotropy constant Ku of 1.2×10⁵J/m³, and a mass magnetization as of 16 A·m²/kg.

The activation volume and anisotropy constant Ku of each of thehexagonal strontium ferrite powder and the ε-iron oxide powder werevalues determined by the above-described method using a vibrating samplemagnetometer (manufactured by Toei Industry Co., Ltd.).

Moreover, the mass magnetization as is a value measured using avibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.)at a magnetic field strength of 1194 kA/m (15 kOe).

Reference Example 1

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that each layer having a thickness shown in Table 1was formed using a support having a thickness shown in Table 1, and theheat treatment in a state where the magnetic tape was wound around thecore for heat treatment, was not performed.

Comparative Example 1

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that the heat treatment in a state where the magnetictape was wound around the core for heat treatment, was not performed.

Comparative Examples 2 and 3

A magnetic tape cartridge was manufactured in the same manner as inExample 1, except that the heat treatment performed in a state where themagnetic tape was wound around the core for heat treatment, wasperformed at a heat treatment temperature shown in Table 1.

Comparative Example 4

A magnetic tape cartridge was manufactured in the same manner as inExample 7, except that the heat treatment in a state where the magnetictape was wound around the core for heat treatment, was not performed.

Comparative Example 5

A magnetic tape cartridge was manufactured in the same manner as inExample 9, except that the heat treatment in a state where the magnetictape was wound around the core for heat treatment, was not performed.

Evaluation of Magnetic Tape

The magnetic tape was extracted from each magnetic tape cartridge of theexamples and the comparative examples 100 days from the date of magnetictape cartridge manufacture, and the following evaluations were performedwith respect to the extracted magnetic tape.

(1) Tape Width Difference (B−A)

The leader tape bonded to the tape outer end was removed, and a tapesample having a length of 20 cm and including the position of 10 m±1 mfrom the tape outer end, and a tape sample having a length of 20 cm andincluding the position of 50 m±1 m from the tape inner end were cut out.The tape width of each tape sample was measured at the center in alongitudinal direction of the tape sample in a state of being sandwichedbetween two sheets of slide glass, in order to remove the effect ofcurl. The measurement of the tape width was performed within 20 minutesafter extracting the magnetic tape from the magnetic tape cartridge,using a laser high accuracy dimension measurement device LS-7030manufactured by Keyence Corporation. In each tape sample, the tape widthwas respectively measured seven times (N=7), and an arithmetical mean offive measured values excluding the maximum value and the minimum valuefrom the measured values obtained in the seven times of measurements wasobtained. The arithmetical mean obtained as described above was set as atape width (tape width A or tape width B) at each position and the tapewidth difference (B−A) was calculated.

(2) Tape Width Deformation Rate

The tape width A obtained by the section (1) was set as a tape widthbefore storage.

The tape sample having a length of 20 cm and including the position of10 m±1 m from a tape outer end was stored in a dry environment at atemperature of 52° C. for 24 hours, in a state where the measurement inthe section (1) was performed, and a load of 100 g was applied in a tapelongitudinal direction, by holding one end portion of this tape sampleand hanging a weight of 100 g on the other end portion. After thestorage, a tape width was obtained within 20 minutes after removing theload, in the same manner as in the method in the section (1), and thistape width was set as the tape width after storage.

A value obtained by dividing a difference of tape widths before andafter storage (tape width before storage−tape width after storage) bythe tape width before storage×10⁶ (unit: ppm) was calculated and set asthe tape width deformation rate.

(3) Tape Thickness

10 tape samples (for example, length of 5 cm) were cut out from a randomportion of the magnetic tape extracted from the magnetic tape cartridge,these tape samples were overlapped, and the thickness was measured. Themeasurement of the thickness was performed using a compact amplifierMillimar 1240 and a digital thickness meter of induction probe Millimar1301 manufactured by MARH. A value which is one tenth of the measuredthickness (thickness per one tape sample) was set as the tape thickness.

The thickness of each layer shown in Table 1 is a designed thicknesscalculated under the manufacturing conditions and the thickness of thesupport is a manufacturer's value.

Recording and Reproducing Test

The magnetic tape cartridge in which the data of regulated capacity wasrecorded on the magnetic tape was stored in the environment of atemperature of 40° C. and relative humidity of 80% for 3 months, and itwas evaluated whether or not the reproducing can be performed in a casewhere the reproducing (reading) of the entire recording data wasperformed. The recording and the reproducing were performed using a LTOUltrium 7 (LTO 7) drive. The regulated capacity is 6.0 TB (terabytes).

The recording of data was performed after placing the magnetic tapecartridge in the evaluation environment 100 days from the date ofmagnetic tape cartridge manufacture, leaving for longer than a day, andexposing to the same environment. In a case where the error occursduring the recording and the recording of the regulated capacity cannotbe performed, the cartridge cannot be used in the subsequent evaluationand shown as “cannot be evaluated” in Table 1. The case of the “cannotbe evaluated” described above is specifically a case where the magnetichead cannot be positioned at a position to be recorded and the drivesends an error signal and stopped, even in a case where a servo patternwas read by a servo head of the drive and the head tracking wasperformed.

After the storage, the reproducing was performed in the environment of atemperature and humidity which are the same as the environment in whichthe recording was performed, and this reproducing was performed usingthe solid drive which is the same as that used during the recording. Thereproducing was also performed after leaving the magnetic tape cartridgein the evaluation environment for longer than a day, and exposing to thesame environment. Regarding the entire data recorded on the magnetictape in the magnetic tape cartridge, in a case where the reproducing wascompleted without the occurrence of the error, “reproducible” was shownin Table 1. In a case where the data could not be properly read from thereproducing signal due to a poor signal-to-noise-ratio (SNR) of thereproducing signal at the time of the reproducing, and the error occursduring the reproducing, so that the reproducing of the entire data wasnot completed, “cannot be reproduced” was shown in Table 1.

The results of the above evaluation are shown in Table 1 (Table 1-1 toTable 1-3).

TABLE 1-1 Example1 Example2 Example3 Example4 Example5 Example6 Kind ofBaFe BaFe BaFe BaFe BaFe BaFe ferromagnetic powder Kind of PEN PEN PENPEN PEN PEN non-magnetic support Thickness of 0.2 μm 0.2 μm 0.2 μm 0.2μm 0.2 μm 0.2 μm non-magnetic layer Thickness of 4.6 μm 4.6 μm 4.6 μm4.6 μm 4.6 μm 4.6 μm non-magnetic support Thickness of 0.1 μm 0.1 μm 0.1μm 0.1 μm 0.1 μm 0.1 μm magnetic layer Thickness of 0.3 μm 0.3 μm 0.3 μm0.3 μm 0.3 μm 0.3 μm back coating layer Tape thickness 5.2 μm 5.2 μm 5.2μm 5.2 μm 5.2 μm 5.2 μm Heat treatment 55° C. 60° C. 70° C. 50° C. 40°C. 45° C. temperature Tape width difference 8.0 10.0 12.0 6.0 3.0 4.0 (B− A) [μm] Storage 310 280 260 360 390 380 deformation rate [ppm]Reproducing Reproducible Reproducible Reproducible ReproducibleReproducible Reproducible Example7 Example8 Example9 Example10 Example11Example12 Example13 Kind of BaFe BaFe BaFe BaFe SrFe SrFe ε-iron oxideferromagnetic powder Kind of PA PA PET PET PEN PEN PEN non-magneticsupport Thickness of 0.2 μm 0.2 μm 0.2 μm 0.2 μm 0.2 μm 0.2 μm 0.2 μmnon-magnetic layer Thickness of 4.6 μm 4.6 μm 4.6 μm 4.6 μm 4.6 μm 4.6μm 4.6 μm non-magnetic support Thickness of 0.1 μm 0.1 μm 0.1 μm 0.1 μm0.1 μm 0.1 μm 0.1 μm magnetic layer Thickness of 0.3 μm 0.3 μm 0.3 μm0.3 μm 0.3 μm 0.3 μm 0.3 μm back coating layer Tape thickness 5.2 μm 5.2μm 5.2 μm 5.2 μm 5.2 μm 5.2 μm 5.2 μm Heat treatment 50° C. 60° C. 50°C. 60° C. 55° C. 55° C. 55° C. temperature Tape width difference 6.010.0 6.0 10.0 8.0 8.0 8.0 (B − A) [μm] Storage 360 280 350 280 310 310310 deformation rate [ppm] Reproducing Reproducible ReproducibleReproducible Reproducible Reproducible Reproducible ReproducibleReference Comparative Comparative Comparative Comparative ComparativeExample 1 Example1 Example2 Example3 Example4 Example5 Kind of BaFe BaFeBaFe BaFe BaFe BaFe hexagonal powder Kind of PEN PEN PEN PEN PA PETnon-magnetic support Thickness of 0.3 μm 0.2 μm 0.2 μm 0.2 μm 0.2 μm 0.2μm non-magnetic layer Thickness of 5.3 μm 4.6 μm 4.6 μm 4.6 μm 4.6 μm4.6 μm non-magnetic support Thickness of 0.1 μm 0.1 μm 0.1 μm 0.1 μm 0.1μm 0.1 μm magnetic layer Thickness of 0.3 μm 0.3 μm 0.3 μm 0.3 μm 0.3 μm0.3 μm back coating layer Tape thickness 6.0 μm 5.2 μm 5.2 μm 5.2 μm 5.2μm 5.2 μm Heat treatment None None 30° C. 80° C. None None temperatureTape width difference 2.0 2.0 2.3 13.0 2.0 2.0 (B − A) [μm] Storage 350500 480 200 500 500 deformation rate [ppm] Reproducing ReproducibleCannot be Cannot be Cannot be Cannot be Cannot be reproduced reproducedreproduced reproduced reproduced

The tape width difference (B−A) of the magnetic tape cartridgemanufactured in the same manner as in Comparative Example 1 was obtainedon 360th day from the date of magnetic tape cartridge manufacture was4.5 μm, and the tape width deformation rate was 400 ppm. From thecomparison between this result, and the evaluation results ofComparative Examples 1, 4, and 5 and Examples 1 to 13 in which the heattreatment in a state of being wound around the core for heat treatmentis not performed, it is possible to confirm that the deformationoccurring in the magnetic tape cartridge over time could be caused inadvance, by performing the heat treatment as in Examples 1 to 13.

In each magnetic tape cartridge of Examples 1 to 13, it was possible toprevent the occurrence of the error to perform the recording andreproducing.

With respect to this, from the comparison between Reference Example 1,and Comparative Examples 1, 2, 4, and 5, it is possible to confirm thatthe reproducing error easily occurs, in a case where the tape thicknesswas decreased to be equal to or smaller than 5.2 μm. In ComparativeExamples 1, 2, 4, and 5, the occurrence of the reproducing error couldnot be prevented, and the reproducing of the entire data cannot becompleted.

It is thought that the reason of the “cannot be evaluated” inComparative Example 3 is because, as the tape width difference (B−A)exceeds 12.0 μm, the width varies depending on the position of the tape,and accordingly, the recording error occurs.

One aspect of the invention is effective in the technical fields ofvarious data storage.

What is claimed is:
 1. A magnetic tape cartridge of a single reel typein which a magnetic tape is wound around a reel, wherein the magnetictape includes a non-magnetic support, and a magnetic layer including aferromagnetic powder on the non-magnetic support, a thickness of thenon-magnetic support is 3.0 to 5.0 μm, a tape width difference B−Abetween a tape width A at a position of 10 m±1 m from a tape outer endand a tape width B at a position of 50 m±1 m from a tape inner end is2.4 μm to 12.0 μm, and the tape width A and the tape width B are valuesmeasured 100 days from the date of magnetic tape cartridge manufacture.2. The magnetic tape cartridge according to claim 1, wherein a tapewidth deformation rate of the magnetic tape measured within 20 minutes,after the magnetic tape is stored in a dry environment at a temperatureof 52° C. for 24 hours in a state where a load of 100 g is applied to atape in a longitudinal direction and the load is removed, is equal to orsmaller than 400 ppm, and the tape width deformation rate is a valueobtained by starting the storage 100 days from the date of magnetic tapecartridge manufacture.
 3. The magnetic tape cartridge according to claim1, wherein the magnetic tape includes a non-magnetic layer including anon-magnetic powder, between the non-magnetic support and the magneticlayer.
 4. The magnetic tape cartridge according to claim 1, wherein themagnetic tape includes a back coating layer including a non-magneticpowder on a surface side of the non-magnetic support opposite to asurface side provided with the magnetic layer.
 5. The magnetic tapecartridge according to claim 1, wherein the non-magnetic support is apolyethylene naphthalate support.
 6. The magnetic tape cartridgeaccording to claim 1, wherein the non-magnetic support is an aromaticpolyamide support.
 7. The magnetic tape cartridge according to claim 1,wherein the non-magnetic support is a polyethylene terephthalatesupport.
 8. The magnetic tape cartridge according to claim 2, whereinthe magnetic tape includes a non-magnetic layer including a non-magneticpowder, between the non-magnetic support and the magnetic layer.
 9. Themagnetic tape cartridge according to claim 2, wherein the magnetic tapeincludes a back coating layer including a non-magnetic powder on asurface side of the non-magnetic support opposite to a surface sideprovided with the magnetic layer.
 10. The magnetic tape cartridgeaccording to claim 2, wherein the non-magnetic support is a polyethylenenaphthalate support.
 11. The magnetic tape cartridge according to claim2, wherein the non-magnetic support is an aromatic polyamide support.12. The magnetic tape cartridge according to claim 2, wherein thenon-magnetic support is a polyethylene terephthalate support.